1. Field of the Invention
The present invention generally relates to a torque converter, such as a hydrokinetic torque converter, which torque converter includes a pump wheel driven by an internal combustion engine, a turbine wheel connected to a driven shaft, and a stator, which together form a converter circuit filled with hydraulic fluid, preferably oil. The torque converter also includes a lock-up clutch, which lock-up clutch has at least one piston, which piston can be connected by means of at least one friction lining to the converter housing. The piston, along with the converter housing, defines a chamber, whereby the chamber is connected by at least one flow guide to a passage. The at least one flow guide can he disposed essentially radially with respect to the passage, and the passage can preferably extend essentially axially in the driven shaft. The torque converter also generally includes a supply system with switchable feed and discharge lines, wherein at least one of the lines runs to the passage and the another of the lines runs to the converter circuit to feed the converter circuit.
2. Background of the Invention
A torque converter, of the type described above, is disclosed in German Patent Application No. 41 21 586 A1, which corresponds to U.S. Pat. No. 5,215,173, according to which oil can be fed by means of a hollow support shaft from a reservoir to the converter in a first flow direction, which results in a connection of the piston of a lock-up clutch to the converter housing by means of at least one friction lining. For a second flow direction of the oil in which the piston is separated from the converter housing, a driven shaft oriented coaxially to the support shaft carries the flow in the area of a passage in the form of a longitudinal hole. In the latter case, after the oil flows through a space connected to the output side of the longitudinal hole and a flow guide which runs radially outside the longitudinal hole, the oil is transported into a chamber formed between the converter housing and the piston. In this case, the space connected to the output side of the longitudinal hole is designed, with respect to the axis of rotation of the driven shaft, so that it has a diameter which is significantly smaller than the diameter of a second space which is also connected to the longitudinal hole in the driven shaft, from which second space a throttle leads to the side of the piston facing away from the converter housing.
As a result of the smaller diameter of the first space, and the resulting flow guide which extends far radially inward, it is possible to prevent an overflow of the oil which accumulates in the second space into the flow guide, and thus into the chamber.
When the piston separates from the converter housing, some of the oil guided through the longitudinal hole in the driven shaft is pumped by means of the throttle hole between the piston and the turbine wheel.
This oil is intended to cool the piston, principally in the vicinity of the friction surfaces, which is important primarily when the lock-up clutch is in slip operation. But that presents the following problem:
The flow of oil, since it comes into contact with the piston in the vicinity of the interface between the turbine wheel and the piston, exerts its cooling action radially deep inside the friction lining, so that it is essentially not possible to sufficiently reduce the heat which occurs at the friction lining. In the vicinity of the at least one friction lining, the piston and the piston housing can therefore become so hot that the oil can break down in this area.
European Patent Application No. 0 428 248 A2 discloses an additional torque converter with a look-up clutch in which the piston is operated with a specified slip. To be able to dissipate the heat which is generated in the area covered by the friction lining on converter elements such as the piston or converter housing, channels are formed in the friction lining along the entire circumference which channels run radially outward, starting from a connection opening to the converter circuit on the side of the piston facing the turbine wheel. The oil used to cool the friction lining is transported via the channels from the converter circuit, over or through the friction lining, end into the area radially outside the piston, where it can be fed back into the converter circuit.
As a result of such a configuration of the friction lining, it is of course possible to cool the converter elements in the vicinity of the friction lining, but it is essentially not possible to cool a large surface area. The oil which has been heated after flowing through the friction lining is also returned to the converter circuit, which can be considered to be a disadvantage.